The LDM sequence-space helper was already implemented in Rust, but C still
owned the public symbol and forwarded through a pointer-based Rust bridge.
Make the Rust parameter representation public and ABI-compatible for the
original by-value `ldmParams_t` call, then have Rust compare `enableLdm`
directly with `ZSTD_ps_enable` before applying the sequence bound. Remove only
the redundant C bridge declaration and wrapper; table sizing, state, and
sequence generation remain unchanged.
Test Plan:
- `git diff --check` -- passed.
- `git diff --cached --check` -- passed.
- `cc -std=c99 -Ilib -Ilib/common -Ilib/compress -Ilib/decompress -Ilib/dict -fsyntax-only lib/compress/zstd_ldm.c` -- passed.
- `cargo +nightly fmt --manifest-path rust/Cargo.toml --all -- --check` -- passed.
- Cargo build/test, make, and other heavy checks were intentionally not run per the requested lightweight-only scope.